1. Field of the Invention
The present invention relates to a descaling method and a descaling apparatus, more particular to a descaling method and a descaling apparatus that apply high-pressure fluid to remove the scale on the surface of semi-finished products (referred as rolling stock) in the hot rolling processes, such as the rolling of steel strip, steel plate, shaped steel, steel bar, wire rod, etc., for descaling purpose.
2. Description of the Related Art
In general, the scale on the surface of the rolling stock must be removed preceding rolling to prevent from the rolled-in-scale defects in a conventional hot rolling process such as for steel strip or steel plate. Therefore, a high-pressure fluid descaling apparatus is usually arranged before the rolling machine.
FIG. 1(a) shows the schematic drawing of the impact regions formed by the ejection of the nozzles of the conventional high-pressure fluid descaling apparatus; FIG. 1(b) shows the schematic drawing of the arrangement of the descaling apparatus; FIG. 1(c) shows the side view of a conventional high-pressure fluid descaling apparatus. In FIG. 1(a), B is the jet width, E is the nozzle distance, O is the overlapping, γ is the offset angle of the nozzle axis against the header axis. In FIG. 1(b), α is the nozzle spray angle, and β, in FIG. 1(c) is the inclination (lead) angle.
As shown in FIGS. 1(a) to 1(c) for a conventional descaling apparatus, the inclination angle β is to lead the scale up-stream so as to prevent from rolled-in-defects in rolling stock such as the steel strip or the steel plate. In other words, general conventional descaling flushes the scales away against the rolling stock transportation direction, and the inclination angle β is generally about 15°.
FIG. 2 shows the A-A cross-section of FIG. 1(b) about the overlapping of the jet spray of the conventional adjacent nozzles; FIG. 3 shows the rebounding of the jet spray of the conventional nozzles, in which X is the diverging angle due to the rebounding; FIG. 4 shows the usage of an aluminium plate in the erosion experiment of two adjacent impact regions, in which G is the width of the blank region and W is the width of the softened region after being eroded.
As shown in FIGS. 1(a) to 3, the jet curtains 12, 13 out of nozzles 11 are diverged by the offset angle γ to prevent them from interfering with each other, thereby decreasing the uniformity of descaling. The impact regions 14, 15 on the surface of the rolling stock 10, which are formed by the jet curtains 12, 13 ejected by the consecutive nozzles 11, are partly overlapped so as to remove the scale evenly. However, having performed erosion test repetitively by using an aluminium plate as a testing plate, the testing results are not to the anticipation. It turns out as shown in FIG. 4 that the impact regions 14, 15 of the adjacent nozzles 11 do not overlap and there is a blank region (G) created, in which there is no erosion effect.
The blank region (G) occurs mainly because the rebounding fluid 16 from the jet curtain 13 behind the overlapped region interferes with the jet curtain 12 ahead of the overlapped region as shown in FIG. 2. Part of the jet curtain 12 may not effectively reach the overlapped region on the aluminium test plate; hence, the impact force is greatly reduced. Another important reason is that the rebounding fluid tends to extend towards two sides where there is less pressure. As a result, the rebounding fluid 16 will diverge outwardly as shown in FIG. 3.
In the blank region (G), only slight mark appears. In the softened region (W), rough surface is formed on the aluminium testing plate, whereas the width and depth of the erosion mark becomes narrower and shallower. In other words, the impact force or descaling effect to the blank region (G) and the softened region (W) is diminished due to the interference caused by the rebounding of the jet sprays from the adjacent nozzles.
The existence of the blank region (G) and the softened region (W) shows that the conventional high-pressure fluid descaling nozzles 11 are not adequately arranged, which is one of the main reasons why the scale is rolled in. However, in respect to the conventional technology, the problems are often deemed improper arrangement of the nozzles 11 or improper arrangement of the descaling apparatus, which causes the insufficient overlap of the impact regions 14 and 15.
Therefore, it is innovative to provide a high pressure fluid descaling method and apparatus for the hot rolling process to reduce the interference on the overlapped region, in which the rebounding fluid emerged from the jet curtains of the adjacent nozzles.